1. Field of the Invention
The present invention relates to a cordless telephone apparatus including a base unit and a sub unit connected with each other by wireless, and more particularly, to a telephone apparatus provided with a function to retrieve and transmit telephone number data stored in the apparatus.
2. Description of the Prior Art
In recent years, a cordless telephone apparatus has rapidly been spreading which includes a base unit connected to the telephone line and a sub unit connected to the base unit by wireless. In such a telephone apparatus, calls can be made with the sub unit at a place away from the base unit by connecting the sub unit to the telephone line through the base unit.
Generally, the base unit is also provided with the transmitting and receiving functions, so that calls can be made not only with the sub unit but also with the base unit. In this case, to protect the privacy, it is necessary to take some measures to prevent the contents of calls made with the base or sub unit from being monitored through the other unit. For this purpose, for example, Japanese Published Patent Application H4-8983 discloses a cordless telephone apparatus where the access from the sub unit is inhibited when the base unit is busy.
A telephone apparatus is widely used which has a directory function to reduce the number of operations for calling by registering and storing a plurality of frequently called telephone numbers in the telephone apparatus and retrieving a registered telephone number by a few key operations. With such a telephone apparatus, the time required for the connection to the telephone lines is reduced and the mis-input of telephone numbers is prevented, so that calling is efficiently performed. The telephone numbers to be registered are stored in a rewritable memory area called a directory area, and modifications such as addition, change and deletion can be made by the user.
A telephone apparatus has also spread which has a callers function to store callers' telephone numbers. At a switching station in a telephone service facility, the telephone number data of the caller is transmitted during a dormant period when the reception signal is transmitted to the receiver. The telephone apparatus of the receiver receives and automatically stores the telephone number data. The callers' telephone numbers are stored in a memory area called a callers area and displayed by an operation by the user. Thereby, the user can find the telephone number of a caller who made a call in the user's absence. Further, the displayed telephone number can be used to place a call, so that it is unnecessary to input the number. A plurality of numbers can be stored, and the addition and deletion of numbers are possible since the callers area is also rewritable.
When a cordless telephone apparatus is provided with the function to store telephone numbers, the callers area and the directory area are normally provided in the base unit. The display for displaying a telephone number is usually provided in the sub unit which is more frequently used. Thus, the user accesses the memory area of the base unit from the sub unit to refer to the telephone numbers stored therein. Since the sub unit is desirably small-sized and lightweight, the size of the display provided in the sub unit is reduced to the extent that information on one telephone number can be displayed.
In such an arrangement, the base unit receives a telephone number reference request from the sub unit, and retrieves one telephone number from the memory area to transmit the number. In the sub unit, the number transmitted from the base unit is displayed by the display. When the telephone number is not the necessary one, the user transmits a reference request again. The base unit retrieves another telephone number and transmits it. This operation is repeated until the necessary telephone number is displayed.
As the method to retrieve a telephone number in the directory area, for example, the following methods are known: a method as disclosed in Japanese Laid-open Patent Application No. S64-89847 where a key word such as the name is stored together with the telephone number and the telephone number is retrieved with reference to the key word; and a method as disclosed in Japanese Laid-open Patent Application No. H3-171857 where the telephone numbers are divided into groups.
According to these methods, however, since more frequently called telephone numbers are not always retrieved sooner, the retrieval takes a long time, and many steps of operations are required. To solve this problem, the Applicant of the present invention proposes in Japanese Laid-open Patent Application No. H4-144345 a method to display the telephone numbers in the order of the number of placing calls. In this case, the number of placing calls is stored together with the telephone number and increased by one every time the number is called. The retrieval is made with reference to the number of placing calls recorded in the telephone number data. According to this method, more frequently used number are retrieved sooner, so that the time required for the retrieval and the number of operations by the user are reduced on the average, whereby the efficiency in placing a call improves as a whole.
The retrieval of telephone numbers in the callers area is normally made based on a reception time. Specifically, a telephone number of the earliest call is retrieved first, and thereafter, telephone numbers are retrieved in the order of reception time.
Telephone apparatuses are on the market which are provided with both the directory function and the callers function. The telephone number data stored in the directory area and the telephone number data stored in the callers area are separately controlled. For this reason, the calling by use of the callers function has no effect on the telephone number data in the directory area. This is a serious problem when the retrieval from the directory area is made based on the number of placing calls. That is, since the number of placing calls of the telephone number data in the directory area is not renewed when a call is placed according to the callers function, the retrieval is not made in the correct order in the retrieval from the directory area. Then, this function is meaningless.
In the telephone apparatus where the access from the sub unit to the base unit is inhibited when the base unit is busy, the telephone numbers in the callers area cannot be referred to and the data in the directory area cannot be modified when the base unit is busy. There is a private telephone system including a main apparatus connected to the public telephone line and a plurality of terminal telephone apparatuses connected to the main apparatus, where information stored in the main apparatus can be referred to from the terminal apparatuses. In such a private telephone system, the terminal telephone apparatuses may be cordless telephone apparatuses each comprising a base unit and a sub unit. However, if the access from the sub unit is inhibited when the base unit is busy, it is impossible to access the main apparatus from the sub unit, so that the information stored in the recording medium of the main apparatus cannot be referred to.
Some sub units are designed so that the receiver's telephone number to be called is displayed by the display when a call is placed. This enables the user to confirm the telephone number before calling. The telephone number is displayed when a call is placed with the base unit as well as with the sub unit. In a cordless telephone apparatus having a base unit provided with no display, when a call is placed with the base unit, the telephone number to be called is confirmed through the display on the sub unit, if the sub unit is placed nearby.
However, the base unit is frequently used when the sub unit is away from the base unit. In such a case, it is a useless irradiation of the electric wave and a waste of electric power to cause the sub unit to display the telephone number which cannot be seen by the user. Further, it is a problem in the protection of privacy that the display of the telephone number to be called is displayed on the sub unit.
Thus, in conventional cordless telephone apparatuses have various problems in the control of the telephone data and in the efficiency in the data transfer between the base and sub units.